Almost invariably, industrial manufacturing processes produce waste liquid streams. This is particularly the case for industries such as those involved in power, mineral, paper, petrochemical, pharmaceutical, food processing, and electronic component manufacture, just to name a few. Most of the waste liquid streams emanating from such processes are waste water streams which are characterised by a range of impurities (and concentrations thereof) which are particular to the specific manufacturing process. For instance, the production of potable water through filtration based desalination of sea water produces a waste water stream which is characterised by having a high concentration of various salts.
Traditionally, a popular way of treating waste water streams has been to separate the solid impurities from the water by evaporation. This is typically achieved on an industrial scale by discharging the waste water stream into large evaporation ponds. The major disadvantages of doing so, however, come from the fact this process is extremely slow, allowing for the possibility that toxic impurities may leach into the soil and/or enter a subterranean water table. Also, when new industrial scale plants are designed, it is often quite difficult to accommodate space for suitably sized evaporation ponds to meet the demands of the industrial process.
Many countries around the world have implemented strict guidelines as to the processing of waste water streams in line with environmental concerns. One measure taken has been the implementation of zero liquid discharge (ZLD) policies to eliminate or at least minimise the liquid waste streams and if possible to recover the liquid (most often water) for reuse or safe disposal.
The technologies currently associated with ZLD include the treatment of the waste water by reverse osmosis, flocculation/coagulation, resin based separation technology, and distillation as well as combinations of these technologies. One of the main issues for implementing many ZLD technologies involves the added capital expenditure and increase in the plant footprint. In relation to capital expenditure, it will be appreciated that any ZLD system would require an additional energy source which in turn may impinge on the environmental benefits of including such systems into existing industrial plants.
The present invention seeks to overcome some of the shortcomings of the known ZLD systems and processes.